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MathGroup Archive 2007

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Re: Expansion symbolic

  • To: mathgroup at smc.vnet.net
  • Subject: [mg74754] Re: Expansion symbolic
  • From: "Dominic Jackson" <dr.kjackson at gmail.com>
  • Date: Wed, 4 Apr 2007 03:54:52 -0400 (EDT)

Could anyone please tell me how to instruct Mathematica to expand the
expression below with respect to the powers of x.  I would like the
constants c1,c2,c3 and c4 to stay behind the summation sign but the powers
of x to cross over to multiply x^(k+i).



(c1 (x^2) +c2 (x^3))* D[(Summation sign i=0 to infinity) Subscript[a,i+1][k]
* x^(k+i),{x,2}]//Expand.



This is what I get



c1 x^2 *(Summation sign i=0 to infinity) (k+i)*(k+i-1) *Subscript[a,i+1][k]
* x^(k+i-2)



+ c2 x^3 *(Summation sign i=0 to infinity) (k+i)*(k+i-1)
*Subscript[a,i+1][k] * x^(k+i-2)



And this is what I want to achieve.



c1 *(Summation sign i=0 to infinity) (k+i)*(k+i-1) *Subscript[a,i+1][k] *
x^(k+i)


+ c2 *(Summation sign i=0 to infinity) (k+i)*(k+i-1) *Subscript[a,i+1][k] *
x^(k+i+1)

Any clues.
Thanx.

Dom


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